Further studies of hydrogenation, disproportionation, desorption and recombination processes in a Nd 5Fe 2B 6 boride

Abstract

The hydrogen absorption and desorption characteristics of, Nd 5Fe 2B 6 were studied in this work, particularly at high temperatures where the hydrogenation, disproportionation, desorption and recombination (HDDR) process takes place. Two events of hydrogen absorption were observed for the ρ-Nd 5Fe 2B 6 compound when heated in hydrogen ( p(H 2)=1 bar). In the lower temperature region (from 335 to 745°C) the formation of an insertion type rhombohedral hydride Nd 5Fe 2B 6H x was observed, leading to a rather small anisotropic lattice expansion (up to 2.63 vol%) in the [001] direction. At temperatures higher than 745°C, a disproportionation of this hydride occurs resulting in the formation of NdH 3− x , NdB 4 and η-Nd 1.1Fe 4B 4. The recombination of the three phase mixture proceeds readily on heating in vacuum, employing conditions similar to those applied in the HDDR route for Φ-Nd 2Fe 14B.